Process for hydrofluorination of acetylenic hydrocarbons



United States Patent 8 Claims. ci. Mil-653.4)

This invention relates to the hydrofluorination of acetylenic hydrocarbons and it relates more particularly to the hydrofluorination of acetylene While in gaseous phase.

It is well known to prepare vinyl fluoride by the action of hydrofluoric acid on acetylene, in gaseous phase, in the presence of a catalyst which can be a metallic fluoride, and in particular aluminum fluoride, a natural or activated alumina or a mixture of these compounds. Such catalysts are obtained either by impregnation of alumina by means of a solution of metallic fluoride, or by pelleting a mixture of powdered alumina and metallic fluoride with the use of a binder, such as graphite or hydrogenated corn oil. The use of such catalysts leads to reaction mixtures containing, in addition to unreacted acetylene, equirnolar quantities of vinyl fluoride and l,1-difluoreth ane. The use of a catalyst, consisting essentially of aluminum fluoride, also leads to a low yield of vinyl fluoride; moreover, it exhibits the severe drawback of limiting the activity of the catalyst to a very small volume of the catalytic bed and thus creates an undesirable temperature gradient within the reactor.

Another process of hydrofluorination consists in causing acetylene and hydrogen fluoride to react according to the t process previously mentioned, separating the 1,1-difiuorethane from the eflluent for recycle through the same reactor with a predetermined quantity of acetylene, without changing the initial feed in acetylene and in hydrogen fluoride. Although this method provides for an increase in the rate of transformation of acetylene to vinyl fluoride, it requires a greater number of operations for separation and recycling of the difluorethane and it also requires more equipment and controls, particularly for the handling of large volumes of gas and the delicate adjustments between the amounts of ingredients.

It is an object of this invention to provide a new and improved process for the hydrofluorination of acetylenic hydrocarbons and it is a related object to provide a process of the type described which overcomes many of the objectionable features of previous processes of the types described.

More specifically, it is an object of this invention to provide a process of the type described in which greater selectivity is achieved in the fluorination of acetylenic hydrocarbon reaction and which produces a higher yield of fiuorinated olefins; which otters the advantage of achieving a more efiicient and effective use of the means employed by lowering the temperature gradient resulting from more favorable heat exchanges in the catalytic bed and which thereby broadens the reaction zone in the catalytic bed and which also avoids the necessity for recycling to achieve a desirable yield of the intended end product.

In accordance with the practice of this invention, the hydrofluorination of acetylenic hydrocarbons, and particularly acetylene, while in the gaseous phase, is carried out by bringing a mixture of hydrofluoric acid and the acetylenic hydrocarbon in the proportions of hydrofluoric acid to hydrocarbon of unity or slightly above when based upon molar ratios, into contact with a catalytic mass at a temperature within the range of 200 C. to 400 C., and preferably 240 C. to 300 C., and wherein the catalytic mass consists essentially of a mixture which includes a diluent such as practically inert sintered alumina and a catalytic agent, in which the diluent is present in an amount within the range of 50% to 95% by volume of the catalytic mass and preferably to by volume, and in which the catalytic agent is present in an amount within the range of 50% to 5% by volume and preferably 35% to 10% by volume with the lower amount of catalyst being present with the higher amount of diluent in the order set forth, and vice versa.

The sintered alumina, employed as the diluent, is characterized by the following:

Total porous volume of between 5 and 50 cm. per g.

of alumina.

Specific surface area of between 0.01 m. g. and l mF/g.

The thermal conductivity of the mixture making up the catalytic bed is suflicient to secure removal of the heat of reaction evolved during the hydrofluorination.

As the catalytic agent, it is preferred to make use of aluminum fluoride prepared by the fluorination of a solid aluminum derivative, such as activated alumina, aluminum nitrate and preferably an anhydrous aluminum derivative such as an aluminum halide and preferably aluminum chloride. Such catalytic agent can be prepared by processes well known to the art, such for example as by re action of gaseous hydrofluoric acid and/ or fluorine (which might be diluted with an inert gas such as nitrogen) with said aluminum derivative at a temperature below the thermal decomposition temperature of any of the reactants and for a period of time sufficient to convert the aluminum derivative to aluminum fluoride.

In another method that can be used for the preparation of the catalytic mass in accordance with the practice of this invention, pieces of aluminum compound to be fluorinated and porous sintered alumina are mixed and then treated with a gaseous stream of hydrofluoric acid and/or fluorine until the aluminum compound is transformed in situ to the corresponding aluminum fluoride. In the preferred practice the preparation of the catalytic mass as described above is carried out in the same reactor in which the hydrofluorination is to be carried out whereby the hydrofluorination reaction can be conducted in the same reactor immediately after the preparation of the catalytic mass.

The granulometry or particle size distribution of the components of the catalytic mass is selected to achieve .optimum thermal conductivity on the one hand and is a desired resistance to attrition on the other hand.

The following example is given by way of illustration, but not by Way of limitation, of the invention:

Example 1 Two volumes of anhydrous aluminum chloride having a particle size of 2 to 10 mm. are intimately mixed with five volumes of balls of 2 to 5 mm. diameter of porous sintered alumina, the main characteristics of which are A stainless steel tubular reactor of 3 cm. external diameter and 1.50 m. long is loaded with 800 cm. of the above mentioned prepared mixture. This mixture is then treated with a gaseous current containing an equimolar proportion of nitrogen and hydrofluoric acid, at a flow rate of 2 moles per hour, and at a temperature not excecding 100 c. and for hours. The fluorination reaction is completed by prornixture'thus treated constitutes the catalytic mass to be a time ranging from 10 to 12 withthe catalyticmass E which contains porous sintercd alumina as a diluent.

It will be apparent from the foregoing that we have provided a marked improvement in the method for the formation are substantially constant as the test time inj creases when eatalystsC, D and E. are employed.

The catalytic composition D is not satisfactory because H it favors the transformation of excessive quantities of tars -on the charcoal surface. This tar formation isnegligible 7 employed. 7 V a l 5 fluorination of acetylenic hydrocarbonsrand particularly The reaction for the hydrofluorination of acetylene is in the preparation of vinyl fluoride as a final product from 7 carried out by fixing the temperature of the reactor at the fluorination of gaseous acetylene. t 280 C. by means of an electric furnace and by passing 'It will be understood that various changes may be a gaseous mixture of acetylene and hydrofluoric acid made in the details ofthe formulationgmaterials and through the reactor, at atmospheric pressure, in 'e'qui- 10 equipment without departing from the spirit of the invenmolecular proportions and in an amount to establish a tion, especially as defined in the following claims. space velocity of about 110 volumes of gas per volume We claim: t a of catalyst per hour. Under these conditions, the tern- 1. In the process of hydrofluorination of an acetylenic perature of the reaction zone is maintained below 300 hydrocarbon, the steps of contacting'a mixture of hydro- C. and with a relatively uniform temperature distribution fluoric acid and acetylenic hydrocarbon with a. catalytic through the catalytic mass. Analysis of the gases evolved, mass'at a temperature within the range of 200 C. to after eliminating unreacted acid, indicates an 80% rate 400C, and wherein the hydrofluoric acid and acetylenic of transformation of acetylene into organic fluorinated hydrocarboni arepresent in the ratio calculated on a derivatives containing 78% molar of vinyl fluoride and molar basis of hydrofluoric acid to racetylenic. hydrocar- 22% molar of 1,1-difluorethane. These values are mainbon of at least unity and wherein the catalytic mass contained over more than 200 hours of continuous 'o emsists essentially of a mixture formed of at least 50 percent tion of the catalytic mass. I by volume but not more than 95 percent by volume of .For purposes of comparison and to illustrate the ima Substantiallyineftrpofous, sihieled aluminflas a d t provements obtained by the practice of this invention, the free of catalytic effect and having a' porous volume of 5 following table summarizes the results of different tests 25 t0 50 CHI-W100 grams and Specific surface of i carried'out in accordance to the process of the invention 1 111. gram and uniformly distributed throughout the as compared to other well known processes: catalytic mass, and a catalytic agent.

' Catalysts Parameters A B o V D E V MolarratimHFlCzH 1.6-1.8 2 2, 1 2 1 Space velocity of the re actants (v./v.lh.) 73-77 85 85 110 110 110 Temperature of the walls of e I the tubular reactor C.). 270 300 260 300 240 240' 240 240 280 Temperature of the Warm zone C.) 305 320 325 340 320 340 300 290 300 i ff?i f?iffii--. 5 5 5 6 3 4 35 -55 7 Duration of the test (h.) 40 40 150 110 60 150 Rate of transformation of 02H: (percent by volume) 82 40 50 t 80 67 85 80 Yield in vinyl fluoride (percent by volume) 54 60 30 55 30 '52 e0 40 78 Yield in 1,1-difluorethane (percent by volume) 46 40 7O 45 it 70 48 40 60 22 u f In the above table: a I 2. In the process of hydrofluorination of an acetylenic i hydrocarbon, the steps of contacting a mixture of hydro- A.A1F3 (8.1% by welght) pellet? Wm} 3 3 fi fiuoric acid and acetylenic hydrocarbon with a catalytic of m l alumma (15% y Welg an grap t6 7 mass at a temperature within the range of 200 C. to

(4% Welght): 5O 400 C. and wherein the hydrofluoric acid and acetylenic B Actlva.lted. alumma' hydrocarbon are present in the ratio calculated on a molar C A1F3 places basis of hydrofluoric acid to acetylenic hydrocarbon of DA1F3 diluted i charcoal. ,at least unity, the'improvement wherein the catalytic mass 'E A1F3.d11utef1 Wlth Porous smtered alumma acgordmg consists of a mixture of practically inert, porous, sintered t0 the mventlon' a 55 alumina as diluent having a total porousrvolume of be-. I V./v./h.-Gaseous volume per volume of catalyst and wants torso cmfi/loo grams and a Spam-fie Surface of Per hour' 7 V I 1 between 0.01 and 1.0 m. gram and uniformly distributed The catalysts A, C, D and E Were prepared by the acthroughout the catalytic mass, and aluminum fluoride, tion of a current of hydrofluoric acid, either diluted or and in-which the materials are present in the mass'in the not diluted by'nitrogen, on activated alumina or on an- 60 ratio of 50 to 95 parts by volume of the porous sintered hydrous aluminum chloride. In all cases the fluorin'ation alumina t0 5 to 50 parts by volume of aluminum fluoride. is completed at 300 C. V V v .3. In the process of hydrofluorination of an acetylenic Results of supplementary tests, carried out' on the y b the s p of O Ct g a mixture f hydroabove mentioned catalysts, and which are not mentioned 7 fiuoric acid and acetylenic hydrocarbon Witha catalytic in the preceding table, show a progressive decrease in the :65 mass a temperature 'w h t r ge 0. Cr to rate of transformation of acetylene in the course of time. and wherein 3 hydrofluoric acld and acetylenic Thus at 30m C. this rate oftransformation reaches about hydrocarbon are Present in theratio calculated o a -35% in volume after an 80 hour period or test with catmolar a of yd qfl c c d y n yd c aylst A'an d about 42%. in volume after hours test Tbon at least r y. the p w n t e with catalyst B. On the other hand, the rates' of trans- 70 catalytw mass consists of a mlxture of practlcally t,

porous, sintered alumina-as diluent havinga total porous volume of between 5 to 50 cm. 100 grams andja specific surface of between 0.01 and 1.0 m. gram and uniformly distributed throughout the catalytic mass, and aluminum ,fluoride, said catalytiomass obtained in situ in the;

hydrofiuorination reactor by the steps of mixing pieces of said porous sintered alumina with an aluminum compound selected from the group consisting of activated alumina, aluminum nitrate and aluminum halide, treating the mixture with a gas selected from the group consisting of hydrofluoric acid, fluorine and mixtures thereof at a temperature below the decomposition temperature for any of the reactants.

4. The process as claimed in claim 3 in which the gas is diluted with an inert gas.

5. The process as claimed in claim 3 in which the aluminum compound is an anhydrous derivative of aluminum.

6. The process as claimed in claim 3 in which the aluminum compound is an aluminum halide.

7. The process as claimed in claim 1 in which the materials are present in the catalytic mass in the direct References Cited by the Examiner UNITED STATES PATENTS 2,471,525 5/49 Hillyer et a1. 260-43514 2,574,480 11/51 Hillyer et a1. 260---653.4

FOREIGN PATENTS 805,503 12/58 Great Britain.

' LEON ZITVER, Primary Examiner.

DANIEL D. HORWITZ, Examiner. 

1. IN THE PROCESS OF HYDROFLUORINATION OF AN ACETYLENIC HYDROCARBON, THE STEPS OF CONTACTING A MIXTURE OF HYDROFLUORIC ACID AND ACETYLENIC HYDROCARBON WITH A CATALYTIC MASS AT A TEMPERATURE WITHIN THE RANGE OF 200*C. TO 400*C. AND WHEREIN THE HYDROFLUORIC ACID AND ACETYLENIC HYDROCARBON ARE PRESENT IN THE RATIO CALCULATED ON A MOLAR BASIS OF HYDROFLUORIC ACID TO ACETYLENIC HYDROCARBON OF AT LEAST UNITY AND WHEREIN THE CATALYTIC MASS CONSISTS ESSENTIALLY OF A MIXTURE FORMED OF AT LEAST 50 PERCENT BY VOLUME BUT NOT MORE THAN 95 PERCENT BY VOLUME OF A SUBSTANTIALLY INERT, POROUS, SINTERED ALUMINA AS A DILUENT FREE OF CATALYTIC EFFECT AND HAVING A POROUS VOLUME OF 5 TO 50 CM. 3/100 GRAMS AND A SPECIFIC SURFACE OF 0.01 TO 1M.2/GRAM AND UNIFORMLY DISTRIBUTED THROUGHOUT THE CATALYTIC MASS, AND A CATALYTIC AGENT. 